Art of nitrating cellulose by pretreatment of the cellulose



' 45 various purposes,

Patented Oct. 4, 1938 UNITED. STATl IS ART OF NITRATING TREATMENT OF I Fred Bacon Stieg, New

PATENT OFFICE OELLULOSE BY rimrun CELLULOSE York, N. Y., assignorto yonier Incorporated, San Francisco, Calif., a corporation of Delaware No Drawing. Application March 28, 1935,

Serial No. 13,481

Claims. (Cl. 260-146) 25 my invention does not the desirable properties of such as the properties of stability, thermoplasticity or its.

For'purposes of definiteness of description and illustration, I will set forth my invention as applied to cellulose derived from wood, and especially such cellulose when provided in its manufacture in sheet form, but it is to 'be expressly 35 understood that it is not to be limited ,to any such specific application, but extends to all applications where like problems obtain in whole or in part.

At the present time, bulk cotton from cotton are commonly used for producing 40 nitrocellulose, and the period for nitration of such cellulose ordinarily required is about thirty minutes.

In the common the finished product, solubility, viscosity, film-forming capacit is common practice to provide it in sheet form dried on a paper machine. The sheet form of wood pulp is almost universally sold in unbeaten condition, varying in thickness, weight and porosity. ,When wood pulp is pro- 50 duced in this way the sheet is relatively thick and with the physical forms of cellulose commonly nitrated at the present time. Thus, in the nitration of 'wood pulp, as it is commonly produced in pulp mills, difl'iculties are 55 encountered, due to the slow penetration of the I possible to nitrate the acid solutions.

substantially interfere with linters derived production of 'wood pulp for nitrating acid into the sheet and/or the slow rate of nitration and/or non-uniform nitration.

Due to these difiiculties, little progress has been made in nitrating wood pulp in the physical form of pulp sheets as manufactured in a. pulp mill, except where nitrating acid solutions, containing an unusually high ratio of nitrating components, are useda process which is considerably more expensive.

By experimentation,

i. e., one-fourth inch by one-fourth inch squares, for convenience in treating with the said nitrating While such period of nitration varies, depending on the thickness and density 01 the sheet, I have found that a period of time, varying from one and one-half hours to six hours, is required to obtain proper nitration with such pulp sheets.

When referring to the time of nitration, I refer to the time period during which thecellulose is in ,uiacturing nitro-cellulose have their apparatus or equipment as well as number and capacity of units, designed and arranged to permit a period of nitration of about thirty minutes. It is, therefore, highly desirable that any process to manufacture nitrocellulose from wood pulp, shall use 58 ously, it is important that the production capacity of existing nitrating installations should not be reduced.

when applying my invention to the nitration of cellulose from cotton or cellulose from wood the machinery and apparatus for the nitrationsv will be substantially the same as that now installed and employed for the nitration of bulk cotton linters. That is, whe operating according to my invention for the tration of cellulose as applied to the utilization of apparatus and synchronization of units for the various steps involved from the original cellulose to the finished nitrocellulose, it will be found that the apparatus required is substantially the same and of the same capacity per individual step in the process, as that which now prevails in the nitration and purification of nitrated esters, wherein cotton linters is the initial form of cellulose. Primarily I have in mind the chinery and apparatus assembly known as the mechanical dipper" assembly, but it is to .be understood that my invention is to apply to all other machinery and apparatus, intermittent or continuous, capable of Y producing nitrocellulose.v

The displacement process" and "pot method" machinery and apparatus are examples of other installations for batch operation. It is to be expressly understood that, due to the eifect which this preliminary treatment has on increasing facility of nitration and diminishing the period of penetration of nitrating mixture in and through the impregnated cellulose, it is both possible and practicable to utilize the cellulose impregnated according to this invention in a continuousmanner in sheet form, or otherwise, and in a continuous nitrating apparatus.

Sulphite wood pulp and sulphite wood pulp which has been refined to a higher alpha cellulose content may be advantageously used in the practice of my invention. Ordinarily such pulps are produced in a bleached unbeaten form of high whiteness. For convenience in processing in the present nitrating equipment previously described, it is obviously desirable that the wood pulp sheet should be cut up into small pieces, as such form permits handling in the standard equipment with greater ease.v These pieces may be small squares, rectangles, or any other, shape which may be conveniently produced and processed. I have found squares measuring onefourth inch by one-fourth inch to function satisfactorily. I

Briefly and in general, my invention 'may be described as follows: I take cellulose preferably in sheet form, and impregnate it with a water solution ofan inorganic compound or at least bring each particle of cellulose into'intimate association with such inorganic compound. Then, the aqueous portion is removed from said cellulose material, as by drying, until the impregnated cellulose material has a low moisture content, preferably lower'than 2% of water on the basis of bone dry condition. After this operation the sheetmay be cut up into small pieces and nitrated according to standard methods. I have discovered that certain inorganic compounds only and certain classes of-inorganic 7 most common ma- I have found that inorganic water soluble compounds of the element boron, such as acids of boron, comprising meta boric acid, ortho boric acid, pyro boric acid and the anhydride of these acids, also salts of such boron acids, sodium perborate, alkali metal salts of boron acids, water soluble alkaline earth metal salts of boron acids, and or salts of boron acids treated with suflicient mineral acid, such as sulphuric acid, to liberate the boron acid, are p rpeminently efflcient. I have discovered that similar water soluble alkali metal salts of the acids of the elements arsenic, aluminum, manganese and chromium also exert a similar, although somewhat lesser effect in reducing the time of nitration. However, these inorganic compounds are less desirable than the boron compounds previously described, because it is more difficult to eliminate these inorganic compounds from the nitrocellulose during stabilization. I have found no tendency for boron impregnating compounds to remainpresent in the nitrocellulose after nitration and stabilization as commonly practiced.

The following tabulated experiments show clearly the effect of previously impregnating the sheets with a water solution of an inorganic compound, drying the sheets and then nitrating same.

Experiments 1 to 10, inclusive, show that a wide range of nitrating acid compositions can be used to produce a nitrocellulose of any desired nitrogen content or a range of nilrogen contents from the lowest to the highest, found to be advantageous in the art. The time of nitration in each experiment was thirty minutes. Sulphite wood pulp in sheet form refined to an alpha cel-e lulose content of about 95 to 96%, and having a high white color was used in these experiments. This pulp was cut into one-quarter inch squares. It had an original basis weight of two hundred 1 eight pounds and a thickness of .031 inch. The

' Sulphur- Nitric Water Nitration ex: is sold acid content Yield pcriment content content nlof nitronumber of nitrat' olnitrab trating cellulose lng acid ing acid acid Percent Percent Percent Percent Percent 1 51. 00 30. 00 19. 00 143. 2 10. 83 52. 50 30. 00 17. 50 151. 0 11.. 39 3 54. 00 30. 00 15. 159. 5 11. 96 52. 5O 31. 40 16. 160. 0 11. 96 51. 37 33. 22 15. 41 163. 2 12. 02 47. 20 38. 33 14. 47 1M. 4 12. 2G 52. 50 32. 80 14. 70 104. 5 12. 42 21. 35 70. 00 8. 55 166. 1 12. 44 39. 59 47. 65 12. 75 166. 5 12. 49 52. 50 34. 20 13. 30 169. 5 12. 83

In addition, my Experiments 11 and 12 show that, when practicing my invention, the temperature'of the nitrating acid solution can be varied as is the practice when commercially producing nitrocellulose. The time of nitration was thirty minutes. The cellulose was the same as that used in Experiments 1 to 10, inclusive, and

- Further'eirperiments, 13, to 18 inclusive. show the progressive rate of nitration when using this same impregnated pulp. the nitrating acid solution. had the following composition: sulphuric acid 50.00%, nitric acid 84.00%, and diluent 16.00%. i The time of nitrating was thirty minutes.

I L I Yield g? meoan yss Nitration oxporimsnt number nitration gfiigg; onmm H l cellulose Minnie: Percent Percent Experiments, 19 to 29 inclusive, show the effect of using other impregnating. materials and mix- 1 tures of impregnating materials. In all instances the nitrating acid compositions were: sulphuric acid 50%, nitric acid 34.00% anddiluent 16.00%.

The time of nitration was thirty minutes.

Nitratlon Nitrogen experiggg f at eist/sis ment n1 ronumber 081M959 lulosa Percent Percent 19 Bulphitepu1pwith5%boricaoid. 161.2 12.01

20 Sulphite pulp with borax 157.3 11.84

previously treated with H 8 Q4.

21 Sulplute pulp with 5% bone 161.1 12.01

acid and 1% sodium perborate.

22 Sulphite pulp with 4% borax 158.3 11.85

and 1% boric acid. 1

23 Sulphit pulp with 5% boric 158.5 12.00 acid and 1% potassium permangans 24 'Sulpldfite pulp with 5% arsenious 153.3 11.90

ac i

25... 8111123100 pulp with 5% arsenic 151.4 11.49

28 Sulphite pulp with 6% sodium 150.5 11.76

alnminate.

27 Sulphite pulp with 5% DOlIas- 149.3 11.76 slum permanganat p 3 Sulphite pulp with 5% potas 134.2 sium dichromate.

29-.. Sulphate pulp with 5% boi'ic 156.5 11.89

. acid. 1 l

In Experiment #30 bulk cotton (cotton linters) -was impregnatedwith 5% boric acid and nitrated for only twenty minutes with the nitrat ing acid composition: nitric acid 22.50% yield was 165.9% 12.01%. p

In all of the above recorded 30 experiments, it was found that th resulting nitrocellulose was properly nitrated as evidenced by the usual sulphuric" acid 60.00%, and diluent 17.50%. The and the nitrogen content was Nitrocellulose yields mentioned above are yields calculated on a basis of the impregnated cellulose nitrated less the impregnating material In these experiments to the arts is possible.

used. I prefer to use a pulp refined to a higher alphacellulose content. The term "refined to a higher alpha cellulose content" has a definite meaning in the art namely sulphite pulp is of 88% tent. This is refined by processes well known in the art so that a product may be'provided having an alpha cellulose content as desired up to 98 or 89%.

The successor my invention is dependent upon the impregnation of the cellulose with materials having the efiect of facilitating the nitration reaction. From extended experiments I have disto 89% alpha cellulose conrapid and thorough wetting of the cellulose with the nitrating acid solution. I have employed the cellulose prepared for nitratiomwhich was used in Experiments 1 to inclusive, and immersed it in the nitrating acid so ution and have the employment of the cellulose, other factors being equal. This augmentation of acid penetration constitutes an unlooked for and highly important discovery, for by its employment in the art of cellulose nitration, ,a greater productive capacity is possible with a given unit equipment anda more satisfactory and hence more acceptable nitrocellulose Furthermore, with increase of speed of initial nitrating acid penetration comesa more desirable nitration.

Whatever may be the theoretical explanation, it positively remains that the presence of the impregnating compound in the cellulose, and more particularly the compounds of boron, most certainly facilitates nitration by reducing the time of nitration, and

would result if the without the step of impregnating the cellulose Ordinarily wood same or a similar wood pulp sheet previously treated with borlc acid acassociation the compounds herein set forth and cellulosic material.

In my experiments, to demonstrate the advantageous effects of certain water soluble impregnating agents for cellulose, I used acids of boron, salts of acids of boron, and salts of acids of. boron treated with sulphuric acid, also acids of arsenic, aluminates, permanganates, chromates and mixtures comprising two or more of these chemicals. Of the agents used, those containing the chemical element boron gave the most satisfactory results. I prefer to use ortho boric acid, or meta boric acid or pyro boric acid, or the anhydride of these acids, or the water soluble alkali metal salts of the boric acids previously mentioned, or the water soluble alkaline earth metal salts of the boric acids, whose sulphates are also water soluble.

My experiments show that the amount. of these impregnating agents in the pulp have the effect of regulating the time of nitration. In order to bring the time of satisfactory nitration to about thirty minutes, certain amounts of agent on the weight of the cellulose after drying are required, depending on the thickness and density of the sheet. In Experiments 19 and 20, for example, five percent of boric acid was found to give proper nitration in thirty minutes. In general, amounts from 2-5% have. a desirable practical effect. That is, as a generality, amountsof impregnating material of two to five percent by weight, based uponthe air dry weight of the cellulose to be nitrated induces the effect desired. This is especially true wherein such boron compounds as an acid of boron or a salt of the same is.employed. Amounts above five percent of a boric acid as well as other impregnating agents.

were found to give no additional benefit.' Since the impregnating agents, especially compounds of boron, are soluble in the nitrating acid solution, a calculated amount. of the agent was added to the nitrating acid solution in conducting experiments in order that the nitrating acid would contain an amount of the inorganic impregnating agent equivalent to the amount which would accumulate in the nitrating acid in regular commercial practice, where the nitrating acid is constantly strengthened and then reused. However, the presence of the agent in the nitrating acid solution appears to have no objectionable effect. In nitrating procedures I prefer compounds of the chemical element boron as impregnating ma.- terials for the cellulose. Of these I prefer the acids of boron. When impregnating the cellulose, whether by spraying, immersion or by any other means whatsoever, I desire that, subsequent to the removal of water by drying, the inorganic compounds be substantially uniformly distributed throughout the cellulosic material. I. prefer to nitrate the thinnest practical sheet of pulp that can be economically made on a paper machine. I have found that such whole sheet or sheets of any convenient size respond as readily to nitration as do the smaller, onequarter of an inch squares. I prefer nitrating acid compositions, depending upon the percentage of nitrogen desired in the nitro-cellulose, to have the highest practical sulphuric acid content and impregnating the lowest practical nitric acid content. The temperature of the nitrating bath may be varied within the usual commercial limits without affecting the value or operativeness of my invention. In other words, my process in nowise interferes with the manufacturing routine or practice commonly obtaining, but rather conforms to or fits in with said practice. Furthermore, attention is especially called to the fact that. the impregnating chemicals of the pretreatment process constituting my invention, do not interfere or affect practically the usual procedure for controlling the nitrogen content or other properties of the nitrocellulose. It is to be understood that my invention is not to be limited to any specific weight or thickness of pulp or to any specific nitratingacid compositions or temperatures of nitrating acid compositions, or to any definite porosity or nitrating acid receptivity. I have varied the thickness and porosity of the pulp I sheet withincomparatively wide limits, and have found my invention equally applicable thereto.

The size or configuration of the individual pieces of wood pulp to be nitrated is not important. My invention applies as well to the nitration of wood cellulose or other forms of cellulose in rolls of indeterminate lengths, of lengths between the same pieces of small size.

I claim:

1.,The process of nitrating substantially unbeaten sheet sulphite cellulose, refined to a higher alpha cellulose content, comprising subjecting such cellulose to impregnation with a water solution consisting essentially of a boron compound; drying the cellulose; and subsequently subjecting such cellulose to a nitrating acid solution.

2. The process of nitrating substantially unbeaten sheet sulphite cellulose, refined to a higher alpha cellulose content, comprising subjecting such cellulose to impregnation with a water solution consisting essentially of a boron compound; drying the cellulose; cutting such sheets into relatively small pieces; and subsequently subjecting such cellulose to a nitrating acid solution.

3. The process of nitrating sheet sulphite-wood pulp, refined to a higher alpha cellulose content, comprising subjecting said cellulose to impregnation with a solution consisting essentially of a boron compound to provide said sheet with about 5% of said compound (5% by weightof impregnating agent on the weight of the cellulose after drying); drying the cellulose to a .low

water content; cutting said sheets into relatively compound, reducing the moisture content of such treated cellulose, subdividing said sheets into relatively small segments, and then subjecting the cellulose to the nitrating acid solution.

' FRED BACON STIEG. 

